Leptosphaeria maculans has been the scourge of farmers since it was first identified in crucifers - a family of flowering plants that includes cabbages and mustard - back in 1791. Its global spread has seen it cause substantial damage to crops over the last forty years.

In 2003, the fungus, also known as blackleg, resulted in canola crop losses of up to 90% in some parts of Australia.

L. maculans reproduces prolifically, allowing it to quickly mutate into genetically diverse populations rapidly overcoming the effectiveness of new resistant varieties of canola.

Their study, reported in the journal Nature Communications, mapped the 12,469 genes that make up the genetic blueprint of L.maculans. They found the fungus has a patchwork of alternating gene rich and gene poor blocks forming a structure not seen before.

Rich blocks, poor blocks

The genetically-poor regions are caused by genes made inactive by a process peculiar to fungi called RIP (Repeating-induced Point Mutation). This produces high mutation rates through nucleotide substitution of cytosine to thymine and guanine to adenine.

Howlett says the gene poor regions are important.

"Our study revealed it is the location of the disease related genes within the poor DNA, which allows the genes to be readily mutated, lost or gained. This enables the blackleg fungus to cause disease outbreaks on canola varieties with particular resistant genes."

The disease works through proteins called effectors, which attack canola through its leaves before moving to the stems, inhibiting plant defences.

Professor Eileen Scott from the University of Adelaide says the work takes our knowledge of this fungus to the next level.

"By explaining how the disease invades the plant we have a better understanding of what the fungus is likely to do to overcome resistant genes in canola."

Targeting specific genes

Howlett says using information from the genome sequence, researchers have developed molecular markers that can predict whether disease outbreaks will occur.

"If an epidemic is predicted then farmers can plant a different canola variety which will not readily succumb to disease."

Canola breeder Professor Wallace Cowling from the University of Western Australia says the study explains why the fungus can adapt so quickly to new resistant strains, which haven't been grown previously.

"It will eventually help breeders keep ahead of the fungus by understanding how it works in nature."